1. Technical Field
The invention relates to fuel supply devices for internal combustion engines of the kind comprising at least one electrically controlled injector feeding fuel under pressure into the intake manifold of the engine and an electronic control circuit connected to sensors responsive to operating parameters of the engine, particularly the engine speed, and delivering periodic signals of variable duty ratio to the injector.
The invention applies to all so-called indirect injection devices, namely those feeding fuel into the intake manifold of the engine (and not directly into the combustion chambers). The injection may be monopoint, i.e. with a single injector which sprays the fuel at a single point of the manifold, situated upstream of a restriction member; the invention applies to this case but it is particularly advantageous in the case of multipoint injection, provided by several injectors controlled either all simultaneously, or in groups, or else individually, and each opening into a branch of the manifold upstream of a respective intake valve.
2. Prior Art
As a general rule, indirect injection devices have an operation termed "synchronous" during the periods when the engine is operating under steady conditions. A given injector is actuated when the shaft of the engine is in a given angular position In the case of multipoint injection, by injectors controlled individually or in groups, the different injectors (or the different groups) are generally controlled with a relative phase offset, so as to limit the variations of the fuel supply pressure.
The electronic control circuits for the injection device must be designed to ensure satisfactory operation during transitory operating phases. For example, it has already been proposed to replace synchronous injection with asynchronous injection for supplying the motor with additional fuel it needs during acceleration (U.S. Pat. No. 4,573,443). It has also been proposed to substitute synchronous operation with asynchronous operation when the operating parameters of the engine lead to control pulses of the injectors which are considered too weak in the case of synchronous injection (U.S. Pat. No. 4,200,063).
The invention is intended to solve a different problem, that of starting up the engine and, possibly, operating during heating of an initially cold engine, which requires increasing the amount of fuel delivered to the engine. Different solutions have already been proposed. In particular, an additional cold start injector has been used which sprays pressurized fuel very finely into the manifold: this solution requires an addition injector and a considerable fraction of the sprayed fuel wets the walls of the intake manifold, which is unfavorable, especially when the temperature is very low and when the fuel remains as adhering droplets. A more advantageous solution consists, during the starting phase, in continuously injecting low pressure fuel into the manifold (French Patent No. 2,332,431). But even when the fuel jet is thrown directly onto the stems of the intake valves so as to cause it to break up, fuel fractionation may remain insufficient.
U.S. Pat. No. 3,628,510 discloses a fuel injection system having an analog control circuit, which consequently does not include digital storing means. During starting, the control circuit adds supplemental energizing pulses to the regular synchronous pulses, for increasing the amount of fuel delivered to the engine. Spraying is consequently not improved.